1. Field of the Invention
The invention relates to a computer system, and more particularly to reducing the power consumption of a computer system.
2. Description of the Related Art
Power management is an important issue for computer systems. If the amount of power available to a computer system is limited, such as in a battery for a notebook or a handheld computer, reducing the power consumption of the computer can extend the amount of time the computer can be used when operating on battery power. Even if the computer is a desktop computer, more efficient operation can reduce power consumption. For example, when the computer is used for word processing, the utility rate of the processor of the computer may be only 10%, and 90% of the power of the processor is wasted.
FIG. 1 shows the state transition of a computer system conforming to the advanced configuration and power interface (ACPI) conceived by Intel and Microsoft. A computer is designed to operate under four different states. When the computer is in the G0 work state, it operates normally. If the computer is idle for a predetermined period of time, the computer enters the G1 sleep state witch has a reduced power level. In the G1 sleep state, some system context, such as the CPU context and the chipset context, is lost to reduce power consumption. When a key is pressed, or the mouse is moved, the computer system awakes from the G1 sleep state and enters the G0 work state, and the system context is restored.
Computer systems conforming to ACPI, however, only enter the G1 sleep state when idle. The ACPI cannot reduce the power consumption while the computer is working. Additionally, an ordinary computer system operates at a fixed working frequency and under a single operating voltage. If the computer system dynamically decreases the working frequency and lowers the operating voltage according to system behavior or system application, the power consumption of the computer system is reduced even though the computer is working.